Reading waves and their phase gaps

Science · Waves, Light & Sound · ages 16-17

Name ______________________ Date ____________

A progressive wave carries matter along with the energy.
Circle one: True False
Which graph gives the wavelength?
- Displacement against distance
- Displacement against time
- Force against distance
Two points sit a quarter wavelength apart. What is their phase difference?
- 180 degrees
- 90 degrees
- 360 degrees
The path difference is half a wavelength. How do the waves arrive?
- In antiphase
- In phase
- At double amplitude
Two points are three quarters of a wavelength apart. Give the phase gap in degrees.
Answer: ______________
The path gap is one full wavelength. How do identical waves arrive?
- In antiphase
- With zero amplitude
- In phase, crest to crest
A path difference of 1.5 wavelengths arrives. Whole cycles stay in phase. Give the extra phase beyond full cycles in degrees.
Answer: ______________
Two points sit a quarter of a wavelength apart on a wave. Are they in phase?
- Yes, all neighbours are in phase
- Yes, quarter gaps are antiphase
- No, they differ by 90 degrees

Answer key

For grown-ups. Fold this page away before handing over the rest.

False · Only the disturbance travels; the medium bobs in place.
Displacement against distance · Wavelength is a length, so it comes from the distance graph.
90 degrees · A quarter of 360 degrees is 90 degrees.
In antiphase · Half a wavelength is 180 degrees, crest onto trough.
270 · Three quarters of 360 is 270 degrees.
In phase, crest to crest · Whole cycles line up, so crests meet crests.
180 · One full cycle cancels out, leaving half a cycle: 180 degrees.
No, they differ by 90 degrees · Only whole wavelength gaps are in phase; a quarter gap is 90 degrees out.